The invention relates to a high voltage measuring device for measuring the voltage between two spaced-apart points.
High voltage measuring devices for use in power transmission and power distribution plants usually consist of electromagnetic voltage transformers or capacitor voltage transformers (capacitive voltage dividers). Both types are fairly expensive, heavy and bulky, largely due to the high insulation requirements.
Optical voltage transformers are also known. These transformers are all based on point sensors and require complicated high voltage insulation. The measurement is either of the full voltage, requiring advanced high voltage insulation, or at a reduced voltage level, requiring complicated electrode arrangements or capacitive voltage dividers. In all these cases the required high voltage insulation results in bulky and heavy voltage transformers.
The object of the invention is to obtain a voltage measuring device of the kind referred to above, which offers a high measuring accuracy together with a simple design and low price, low bulk and weight, and easy installation.
The measuring device according to the invention measures a voltage as a line integral of the electric field. It uses a poled optical fibre extending between the two points, the voltage between which is to be measured, such as between a power line and ground. Light is transmitted through the fibre. The electric field at any part of the fibre causes a phase shift of the light, and the phase shift will be proportional to the field. The total voltage is measured as a line integral of the electric field by measuring the accumulated phase shift along the whole length of the fibre.
What characterizes a voltage measuring device according to the invention will be clear from the appended claims.